The overall objective is to develop an in vitro means of predicting the response of individual breast cancer patients to chemotherapy. Specifically: development of a battery of rat mammary tumors growing in vitro as multicellular tumor spheroids (MTS); determination of the sensitivity of these tumors to selected drugs both in vivo and in vitro (MTS); performance of initial investigations on the basis of any lack of correlation observed between in vivo and in vitro results; and improvement of our methods for growing MTS directly from breast cancer patient cancer material.